The present invention relates to hydroxyl-containing polyether-polyester block copolymers, their preparation and their use, in particular for producing polyurethanes.
Polyurethanes are produced in large quantities. They are usually produced by reacting polyisocyanates with compounds containing at least two hydrogen atoms which are reactive toward isocyanate groups, in particular polyether alcohols and/or polyester alcohols. For various applications, it would be advantageous to build both ether groups and ester groups into the polyurethane. However, owing to the incompatibility of polyether alcohols and polyester alcohols with one another, it is not readily possible to use these two compounds together in polyurethane formulations. One possible way of remedying this disadvantage would be to use polyols which have both groups in the molecule. EP-A-671 424 describes a process for preparing polyols containing ether and ester groups by reacting polyether alcohols with polyfunctional carboxylic acids. However, this process has the disadvantages that the viscosity rises greatly even during the preparation and the products formed have a high viscosity and high molecular weight.
At present, the customary preparation of polyether alcohols by base-catalyzed or acid-catalyzed alkylene oxide addition can only be carried out using initiator substances which are stable toward the base used, generally potassium hydroxide or Lewis acids. Customary initiator substances are, for example, glycerol, sugar and glycol. Due to their ester bond which is unstable toward aqueous bases and acids, polyesterols cannot be used as initiator substances.
The base- or acid-catalyzed alkylene oxide addition onto polyester alcohols would lead to cleavage of the polyesterol chain and to saponification of the polyester polyol right back to its starting components, i.e. the desired block structure could not be obtained in the subsequent alkylene oxide addition. The polyester-polyether polyol cleavage products formed in this way are difficult to reproduce and do not have a defined block structure.
It is an object of the present invention to provide polyols which have both ether groups and ester groups in the molecule, can be prepared by simple methods and do not have the disadvantages of the reaction products of polyether alcohols with polyfunctional carboxylic acids.
We have found that this object is achieved by use of multimetal cyanide compounds, frequently referred to as DMC catalysts, for the polymerization of alkylene oxides using polyesterols as initiator substances. Cleavage of the ester groups in the polyesterols does not occur under these conditions.
The present invention accordingly provides polyester-polyether block copolymers which can be prepared by catalytic addition of alkylene oxides onto H-functional initiator substances, wherein polyester alcohols are used as H-functional initiator substances and multimetal cyanide compounds are used as catalysts. The products obtained in this way preferably contain hydroxyl groups.
The invention further provides a process for preparing polyester-polyether block copolymers and provides for their use for producing polyurethanes by reaction with polyisocyanates.
Surprisingly, the defined preparation of the polyester-polyether block copolymers of the present invention by addition of alkylene oxides onto polyester alcohols using multimetal cyanide catalysts occurs successfully without redissociation of the polyester alcohols and other secondary reactions. The polyester-polyether block copolymers of the present invention have a narrow molecular weight distribution and a low content of unsaturated constituents.
The polyester alcohols used as starting materials for preparing the polyester-polyether block copolymers can be prepared by methods customary for this purpose.
The polyester alcohols used as starting materials for the preparation of the polyester-polyether block copolymers of the present invention are usually prepared by polycondensation of at least bifunctional carboxylic acids with at least difunctional alcohols. The polyesterols can also be prepared by polycondensation or polyaddition reactions of aliphatic, cycloaliphatic, araliphatic and/or aromatic carboxylic acid derivatives with aliphatic, cycloaliphatic, araliphatic and/or aromatic alcohols.
As carboxylic acid derivatives, preference is given to using compounds having at least two carboxyl groups, e.g. maleic acid, fumaric acid, malonic acid, adipic acid, glutaric acid, succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid and/or their anhydrides and/or their acid chlorides.
As alcohols, preference is given to using compounds containing at least two hydroxyl groups, e.g. butanediol, neopentyl glycol, pentanediol, hexanediol, trimethylolpropane, pentaerythritol, glycerol, ethylene glycol and its higher homologues such as diethylene glycol and triethylene glycol, propylene glycol and its higher homologues such as dipropylene glycol and tripropylene glycol.
It is likewise possible to react hydroxycarboxylic acids and/or their derivatives such as lactones with themselves and/or with the abovementioned carboxylic acid derivatives and/or alcohols. Examples which may be mentioned are glycolic acid, lactic acid, hydroxypropionic acid, hydroxybutyric acid and hydroxyvaleric acid.
Polyester alcohols which are particularly preferred as initiator substances are those based on adipic acid and/or phthalic anhydride and monoethylene glycol, diethylene glycol and/or triethylene glycol, monopropylene glycol and/or dipropylene glycol and/or tripropylene glycol.
Apart from the acids mentioned, it is likewise possible to use fatty acid derivatives, in particular dimeric fatty acid derivatives as are marketed, for example, by UNICHEMA under the name Pripol(copyright), derivatives based on castor oil and polyhydroxy fatty acids such as, for example, polyhydroxy fatty acid PHF 110 from Harburger Fettchemie. Also suitable are xcex1,xcex2-unsaturated carboxylic acids, in particular hydroxy-functionalized xcex1,xcex2-unsaturated carboxylic acids.
Besides direct reaction, esterification or transesterification variants are also known.
If desired, monofunctional alcohols or carboxylic acids can also be used in small amounts in the synthesis.
Furthermore, the carboxylic acids and alcohols may, if desired, bear further functional groups such as alkyl, aryl, amino, sulfonate, thio, phosphonate or acrylate groups.
The reaction of alcohols with free carboxylic acids is preferred for the preparation of the polyesterols. The polycondensation reaction is usually carried out at from 140 to 250xc2x0 under atmospheric pressure or subatmospheric pressure. If desired, the reactions are catalyzed, preferably using acids, Lewis acids and metal salts, in particular titanium- and/or tin-containing esterification catalysts, for example n-butyl titanate, tin(II) octoate or tin dilaurate. The water of reaction is preferably distilled off until the reaction mixture has an acid number of  less than 10 mg KOH/g, particularly preferably  less than 3 mg KOH/g and in particular  less than 1 mg KOH/g. It is also possible in principle to use polyester alcohols having higher acid numbers, since the excess acid groups react with the alkylene oxides. In a further embodiment, the reaction can be carried out under inert gas such as nitrogen or argon in order to prevent product discoloration due to oxidation products. Depending on the use for which the polyester polyols are intended, they have a hydroxyl number of from 0.5 to 500 mg KOH/g, preferably from 10 to 400 mg KOH/g, and in particular from 30 to 300 mg KOH/g. Thus, the polyester polyols preferably have a number average molecular weight Mn of from 250 to 200,000.
A summary overview of the preparation of polyesterols and their use for producing polyurethanes, in particular polyurethane foams, is given, for example, in the Kunststoff-Handbuch, Volume VII, xe2x80x9cPolyurethanexe2x80x9d 3rd edition 1993, edited by Dr. G. Oertel (Carl-Hanser-Verlag, Munich).
If the polyesterol-polyether block copolymers of the present invention are to be used for producing flexible polyurethane foams, they are particularly preferably prepared using polyester alcohols which have a viscosity in the range from 1000 to 40,000 mPa*s at 25xc2x0 C. In particular, use is made of polyesterols based on propylene glycol and/or ethylene glycol and/or their higher homologues.
The preparation of the polyester-polyether block copolymers of the present invention is carried out by addition of alkylene oxides onto the polyester alcohols using multimetal cyanide catalysts.
As alkylene oxides, it is possible to use, for example, ethylene oxide, 1,2-epoxypropane (propylene oxide), 1,2-methyl-1,2-ethoxypropane, 1,2-epoxybutane, 2,3-epoxybutane (butylene oxide), 3-methyl-1,2-epoxybutane, 1,2-epoxypentane, 3-methyl-1,2-epoxypentane, 1,2-epoxyhexane, 1,2-epoxyheptane, 1,2-epoxyoctane, 1,2-epoxynonane, 1,2-epoxydecane, 1,2-epoxyundecane, 1,2-epoxydodecane, styrene oxide, 1,2-epoxycyclopentane, 1,2-epoxycyclohexane, (2,3-epoxypropyl)benzene, vinyloxirane, 3-phenoxy-1,2-epoxypropane, 2,3-epoxypropyl methyl ether, 2,3-epoxypropyl ethyl ether, 2,3-epoxypropyl isopropyl ether, 2,3-epoxyl-1-propanol[sic], 3,4-epoxybutyl stearate, 4,5-epoxypentyl acetate, 2,3-epoxylpropyl[sic]methacrylate, 2,3-epoxylpropyl[sic]acrylate, glycidyl butyrate, metyl[sic]glycidate, ethyl 2,3-epoxybutanoate, 4-(trimethylsilyl)butane 1,2-epoxide, 4-(triethylsilyl)butane 1,2-epoxide, 3-(perfluoromethyl)propene oxide, 3-(perfluoroethyl)propene oxide, 3-(perfluorobutyl)propene oxide, 4-(2,3-epoxypropyl)morpholine, 1-(oxiran-2-ylmethyl)pyrrolidin-2-one, and also any mixtures of these with one another.
Preference is given to using ethylene oxide, propylene oxide, butylene oxide and mixtures thereof.
Alkylene oxides can be added on individually in the form of blocks and, when using more than two different alkylene oxides, in any mixing ratio as mixed blocks. Furthermore, the alkylene oxide mixing ratio can be varied either discontinuously or continuously during the synthesis.
Multimetal cyanide catalysts used are usually ones of the formula (I),
M1a[M2(CN)b(A)c]d.fM1gXn.h(H2O).eL (I),
where
M1 is a metal ion selected from the group consisting of Zn2+, Fe2+, Co3+, Ni2+, Mn2+, Co2+, Sn2+, Pb2+, Mo4+, Mo6+, Al3+, V4+, V5+, Sr2+, W4+, W6+, Cr2+, Cr3+, Cd2+,
M2 is a metal ion selected from the group consisting of Fe2+, Fe3+, Co2+, Co3+, Mn2+, Mn3+, V4+, V5+, Cr2+, Cr3+, Rh3+, Ru2+, Ir3+,
and M1 and M2 are identical or different,
A is an anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate, cyanate, carboxylate, oxalate and nitrate,
X is an anion selected from the group consisting of halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate, cyanate, carboxylate, oxalate and nitrate,
L is a water-miscible ligand selected from the group consisting of alcohols, aldehydes, ketones, ethers, polyethers, esters, ureas, amides, nitrites and sulfides,
a, b, c, d, g and n are selected so that the compound is electrically neutral, and
e is the coordination number of the ligand,
f is a fraction or integer greater than or equal to 0,
h is a fraction or integer greater than or equal to 0.
These compounds are prepared by generally known methods by combining the aqueous solution of a water-soluble metal salt with is the aqueous solution of a hexacyanometalate compound, in particular a salt or an acid, and adding a water-soluble ligand thereto during or after combination of the solutions.
To prepare the polyester-polyether block copolymers of the present invention, the polyester alcohols are firstly mixed with lip the catalyst and then the alkylene oxide or the mixture of alkylene oxides is metered into the polyester alcohol/catalyst mixture. In order to improve the miscibility of the alkylene oxide in relative highly viscous polyesters and thus to improve the alkoxylation, solvents such as toluene, xylene, tetrahydrofuran, acetone, 2-methylpentanone, cyclohexanone, N-methylpyrrolidone or dimethylformamide may, if appropriate, be added to the reaction mixture.
The reaction of the polyester alcohols with the alkylene oxides is preferably carried out at pressures in the range from 1 to 20 bar, in particular from 2 to 10 bar, and temperatures in the range from 60 to 150xc2x0 C., in particular from 80 to 130xc2x0 C. The preparation is also preferably carried out under a protective gas atmosphere, in particular under a nitrogen and/or argon atmosphere. After the addition of the alkylene oxide has been completed, it is usually followed by an after-reaction phase in order to achieve complete conversion of the alkylene oxides. The polyester-polyether block copolymers are then worked up. The polyester-polyether block copolymer preferably have a ratio of ether groups to ester groups in the range of from 0.01:1 to 100:1 and a number average molecular weight range of from 300 to 300,000.
Secondary constituents such as unreacted monomers and volatile compounds can be removed by various methods known to those skilled in the art, for example by distillation, work-up by means of a thin film evaporator or stripping with nitrogen and/or steam.
If appropriate, suspended materials and solids can be removed from the reaction mixture by various methods known to those skilled in the art, for example centrifugation or filtration.
For certain applications of the polyester-polyether copolymers of the present invention, the catalyst can also remain in the end product.
The polyester-polyether block copolymers are preferably used for producing polyurethanes, in particular rigid polyurethane foams, flexible polyurethane foams and thermoplastic polyurethanes. The polyurethanes are produced using methods known per se by reacting the polyols with polyisocyanates. Depending on the desired properties of the polyurethanes, it is possible to use the polyester-polyether block copolymers of the present invention either alone or together with other compounds containing at least two hydrogen atoms which are reactive toward isocyanate groups. Compounds containing at least two hydrogen atoms which are reactive toward isocyanate groups which can be reacted together with the polyester-polyether block copolymers in the reaction with polyisocyanates include polyether alcohols, polyester alcohols and, if desired, bifunctional or polyfunctional alcohols and amines having a molecular weight in the range from 62 to 1000 g/mol, i.e. chain extenders and crosslinkers. Furthermore, it is possible to use catalysts, blowing agents and the customary auxiliaries and/or additives.
Such compounds and processes for producing the polyurethanes are described, for example, in the Kunststoff-Handbuch, Volume VII, xe2x80x9cPolyurethanexe2x80x9d 3rd edition 1993, edited by Dr. G. Oertel (Carl-Hanser-Verlag, Munich).
It has surprisingly been found that the polyester-polyether block copolymers of the present invention increase the compatibility of polyesterols with polyetherols. Mixtures of polyesterols and polyetherols usually separate into different phases, so that such mixtures can only very rarely be processed in industry. The demixing leads to inhomogeneities in the foam, for example streak formation and crack formation at the phase boundary. Such foams are unusable. Surprisingly, mixtures of polyester alcohols and polyether alcohols are stable to phase separation if at least one polyester-polyether block copolymer according to the present invention is additionally used as phase compatibilizer. Such mixtures are homogeneous and can be processed to form polyurethanes without problems. Particularly in the production of flexible polyurethane foams, the use of such mixtures gives very uniform and fine-celled foams.
Furthermore, foams produced using the polyester-polyether block copolymers of the present invention can generally be readily flame laminated.
In addition, the polyester-polyether block copolymers of the present invention can also be used outside polyurethane chemistry. Possible application areas are as crosslinker components in resins such as epoxy resins and polyester resins, as surfactants or as phase compatibilizers in polymer blends. The polyester-polyether block copolymers of the present invention can also be used as thermoplastic polymers. Here, polyester-polyether block copolymers which have no free functional groups in the molecule are preferably employed.
Moreover, the polyester-polyether block copolymers of the present invention can be functionalized by reaction with further compounds, for example by reaction with epichlorohydrin and xcex1,xcex2-unsaturated compounds such as acrylic acid and methacrylic acid.
The polyester-polyether block copolymers functionalized by xcex1,xcex2xc2x1unsaturated[sic] compounds can be crosslinked by various methods known to those skilled in the art.